Contour following apparatus



July 25, 1967 J. BULK 3,333,144

CONTOUR FOLLOWING APPARATUS Filed March a; 1964 2 Sheets$heet 1 Counter G 1 Code converter Code converter Memory J B 2 gvEN'roR.

July 25, 1967 J. BULK 3,333,144

CONTOUR FOLLOW ING APPARATUS Filed March 5, 1964 2 Sheets-Sheet 2 FIG.3

INVENTOR.

United States Patent 4 Claims. (at. 315- This invention relates to a device for following electronically by means of an electron beam the contour of a figure which can be fixed on a screen, said device being provided with a screen, an electron gun directed to that screen, with elements for deflecting beams, with elements for making the point of intersection of the beam with the screen detectable on the said screen, with a detector element positioned near the screen and with couplings between the deflector elements and the detector element.

Such a device is known from the book, Electronic Analogue Computers, by G. and T. Korn, McGraw-Hill Book Co. Inc., New York 1952.

In this known device a deflector element is connected to the output of a sawtooth generator and another deflector element is connected to the output of an amplifier, the input of which is connected to the output of the detector element.

The point of intersection of the beam with the screen in one direction follows contours under the control of the sawtooth voltage, and in a direction perpendicular to the first under the control of the output voltage of the amplifier which is controlled by a photoelectric cell as detector element.

Contours having a shape which is such that the direction of the movement of the point of intersection, which is a result of the sawtooth voltage, would have its sign inverted while following the contour, cannot be followed by the known device.

It is an object of the invention to provide a device, by which it is possible for these contours too to be followed and in which, consequently, the direction of movement may have its sign inverted in either direction.

For this purpose the invention is characterized in that the elements for the deflection of beams are connected via digital analogue code converters with the outputs of bidirectional counters, the inputs of which are connected with the outputs of a control element which together with the counters formsthe couplings and which comprises a first memory for the conditions through which the counters have gone, and which comprises a second "memory for the signal emitted by the element and which is able to control the counters in dependency on the conditions gone through and on the signal and in which the output voltages of the counters determine the coordinates .of the points of a point raster, which give the'possible intersection points of the beam with the screen.

, In one practical embodiment of the device, an element has been used which is capable of emitting a signal of the type zero or one" respectively, according as the pint of intersection falls inside or outside the contour such as for instance, a photoelectric cell, and this device is characterized in that, if the momentary point of intersection fallsinside the contour or outside it, the signal shifts one of the two counters by one step and a new point of intersection is formed, as the case may be either always to the right or always to the left of the line connecting the momentary point of intersection with the preceding pointof intersection, in such a manner that a broken line of raster points is stepped out along the contour.

A possible occurrence is, for the element to detect the same signal three times running, owing to a contour being diflicult to follow by the device.

In that case the three detected points of intersection are followed by a fourth one which coincides with the first point. If this point lies on the contour there is a possibility of the device losing the contour as it were, the beam then persisting in its course through the said four points of intersection.

In order to prevent this, an improved embodiment is characterized in that the first memory is of such a nature that the condition last gone through is kept in it when the same signal occurs three times running, which means that a new point of intersection is formed in a direct line with the line connecting the third point of intersection with the preceding second point of intersection.

When along the contour the direction changes considerably over a short distance, it may nevertheless happens for a point of intersection, which has already been passed through, to be passed through again. In order to prevent this, the second memory is, in addition to this, of such a nature that, if the same signal occurs five times, it is inverted.

It is of course possible to effect the scanning of the contour with the aid of the memories in a manner differing from that according to this embodiment.

, However, this embodiment, with its improvements, has the advantage that it steps along a small number of points, all of which are situated on either side of the contour, so that the stepping along the contour can be completed rapidly.

All of this will be further elucidated hereinafter, with reference to a drawing showing five figures of the embodiment of the invention, in which:

FIGURE 1 shows the fundamental structure of the embodiment.

FIGURE 2 shows the organization of the control element of FIGURE 1.

FIGURE 3 shows a contour which is easy to follow.

FIGURE 4 shows a portion of the contour having a point of the raster on the contour.

FIGURE 5 shows a portion of a contour showinga considerable deviation of direction.

In these figures like reference numerals and letters refer to like elements.

In FIGURE 1 the screen 1 of the electron-beam tube 16 is provided with element 5 (a fluorescent layer) in order to make the point of intersection of the beam with the screen 1 visible.

In the embodiment of the invention the beam emitted by the electron gun 2 can be deflected in two directions, which are at right angles to one another, by the deflector elements 3 and 4. V v

However, a deflection of the beam according to different coordinates, such as, for instance, according to the pole-coordinates radius (r) and angle (z is also possible.

The detector element 6, a photoelectric cell positioned before the screen 1, repsonds to the portion of the screen 1 which is hit by the electron beam and which falls outside the contour of the mask 15.

The deflector elements 3 are connected to a counter 20 via a digital analogue code converter 12.

The deflector elements 4 are connected to a counter 19 via a digital analogue code converter 10.

The inputs 7 and 8 of the counters 19 and 20 are connected to the outputs 21 of the controlelement 22.

The input 23 of the element 22 is connected to the photoelectric cell 6 via a trigger circuit 17 and an amplifier 13.

The operation of the device is as follows:

The digital analogue code converters and 12 respectively translate the conditions of the counters 19 and 20 respectively into voltages which are supplied to the elements 3 and 4 and with the aid of which the electron beam is deflected, the said Ibeam being emitted by the electron gun 2 in such a manner that its points of intersection with the layer 5 on the screen run through the points of the point raster.

The photoelectric cell 6 ascertains whether a point of this raster falls inside or outside the contour of the mask 15. The circuit 17 makes an unambiguous choice of the signal coming from the photoelectric cell 6 as a signal one or a signal zero, dependently on the masks covering the point of intersection of the electron beam or not.

This signal is now processed in the control element 22, to which is connected a pulse generator 24, which emits pulses regularly distributed in time, so-called clock pulses. At each pulse of the generator 24 the output signal of the circuit 17 is processed and one of the counters 19 and 20 is displaced by one step.

FIGURE 2 shows a more elaborated diagram of control element 22. The input a of this element 22 is connected to the input of a gate 25, the output of which is connected to the input of a four bit shift register 26 and with the input of a gate 27. The four outputs 28 to 31 inclusive of the sections of this register 26 are connected to four further inputs of the gate 25.

Normally, the signal supplied at a is simply passed on via the gate 25 to the inputs of the register 26 and the gate 27 at each pulse of the generator 24; if, however, a like signal appears on each of the four outputs 28 to 31 inclusive, that is to say either on all four a one or on all four a zero, then the gate 25 inverts the next signal supplied at a if this sign again is a one or a zero respectively.

All of this has the result that the signal supplied at a, either inverted or not, is fed to an input 32 of the gate 27.

The gate 27 again is under the control of the generator 24. The outputs 35 and 36 of the gate 27 are connected via the memory elements 33 and 34 with the inputs 43 and 44 of the same gate 27.

The outputs 28 to 30 inclusive are connected to the inputs 40 to 42 inclusive of the gate 27. If on the inputs 32, 40 and 41 appear like signals, i.e. either ones or zeroes, the gate 27 blocks. If on the other hand a like signal appears on the inputs 40, 41 and 42, the gate 27 will open, no matter whether on the input 32 there appears a like signal at the same time or not. If the gate 27 is closed, it will block a change of the memory elements 33 and 34 during a pulse from the generator 24. A new condition of these elements 33 and 34 is dependent on the condition on the input 32 and on the conditions on the inputs 43 and 44 of the gate 27, whilst the conditions on the input 40 to 42 inclusive of the gate 27 show the above-described operation, whether blocking or not, of the gate 27.

The above is shown in the subjoined table.

New conditions of the elements 33 and 34 are obtained on the outputs 45 and 46 after each pulse from the pulse generator 24 and they are formed by combining a new signal on 32 with the condition prevailing on the outputs 45 and 46 respectively.

Now the gates 47 and 48 serve the purpose of combining the signals appearing on the outputs 45 and 46 of the memories 33 and 34 in such a way, that either the xcounter 19, or the y-counter 20 advances or retreats by a step.

The signals on the outputs 45 and 46, together with the inverted signal of each, are always at disposal on extra outputs 45' and 46 (not shown in the drawing).

The gate circuits 47 and 48 are arranged in such a way, that, if a signal one appears on both the outputs 45 and 46, the y-counter is advanced by one step. If a one appears on both the extra outputs 45' and 46, then the ycounter 20 is set back by one step. If a one appears on the output 45 and the output 46', then the x-counter 19 advances stepwise and if a one appears on the output 45' and the output 46, the x-counter 19 retreats by one step. Diflicult contours can be followed with a following apparatus equipped with an element according to FIG- URE 2. However, there also exist contours, such as shown in FIGURE 3, which can be followed with a following apparatus provided With a simpler element 22. Of a simpler element 22 applied in this instance it was demanded that it had to displace either of the counters by one step at each pulse from the pulse generator, and that in such a way that the point of intersection of the beam turns to the right if the point read is situated outside the contour and to the left if it is situated inside the contour.

Of course it is also possible to interchange the turning to the left and to the right without any difliculty.

A point outside the contour is indicated by a circle and a point inside the contour by a dot. Difliculties will occur when a situation arises as represented in FIGURE 4. If the point 61 is substantially situated on the contour 60 and if then the point 61 is seen for the first time as lying inside the contour when the dot comes from 62, and for the second time when the dot comes from 63 as lying outside the contour 60, the dot will keep spinning round a small square.

In FIGURE 2 this diificulty was solved by arranging the gate 27 in such a manner that it blocks the memories 33 and 34 if the shift register 26 and the signal on the input 32 represent a definite condition.

Instead of the dot returning from the position 63 to the position 61, the dot advances from the position 63 to the position 64, as indicated by the dotted line.

The same difliculty may arise when the same signal is detected five times running. This is shown in FIGURE 5.

Now the contour 60 can be followed further, because the detected signal is inverted at 65. (The circle indicates that light has been ascertained; yet the dot turns to the left.)

In FIGURE 2 the solution of this difliculty was found in the operation of the gate 25, which is under the control of the four outputs 28 to 31 inclusive of the shift register 26.

I claim:

1. A system for following electronically by means of an electron beam the contour of a figure comprising a screen, an electron gun directed on the screen and having elements for deflecting beams with elements for making the point of intersection of the beam with the screen detectable on the said screen, a detector element positioned near the screen having couplings between the deflector elements and the detector element in a digital analog of the converter and bi-directional counter, the elements for the deflection of the beams being connected by the digital analog code converter with the output of the bi-directional counter and the inputs of which are connected with the outputs of a control element, which together with the counter forms the couplings, a first memory element for the conditions through which the counters have progressed, a second memory for the sig- 5 nal emitted by the control element which is able to control the counters in dependency on the conditions and on the signal, and the output voltages of the counters determining the coordinates of the points of a point raster which impart the possible intersection points of the beam with the screen.

2. A system according to claim 1, in which the element is capable of emitting a signal according as the point of interesection falls inside or outside the contour, wherein if the momentary point of intersection [falls inside the contour or outside, the signal shifts one of the two counters by one step and a new point of intersection is formed, always to the right or always to the left of the line connecting the momentary point of intersection with the preceding point of intersection so that a broken line of raster points is stepped out along the contour.

3. A system according to claim 1, in which the first memory is of such that the condition last gone through is maintained therein when the same signal occurs three times one after the other.

4. A system according to claim 1, in which the second memory is such that a signal which occurs five itmes one after the other is inverted.

References Cited UNITED STATES PATENTS JOHN W. CALDWELL, Acting Primary Examiner.

DAVID G. REDINBAUGH, Examiner.

R. L. RICHARDSON, T. A. GALLAGHER,

Assistant Examiners. 

1. A SYSTEM FOR FOLLOWING ELECTRONICALLY BY MEANS OF AN ELECTRON BEAM THE CONTOUR OF A FIGURE COMPRISING A SCREEN, AN ELECTRON GUN DIRECTED ON THE SCREEN AN HAVING ELEMENTS FOR DEFLECTING BEAMS WITH ELEMENTS FOR MAKING THE POINT OF INTERSECTION OF THE BEAM WITH THE SCREEN DETECTABLE ON THE SAID SCREEN, A DETECTOR ELEMENT POSITIONED NEAR THE SCREEN HAVING COUPLINGS BETWEEN THE DEFLECTOR ELEMENTS AND THE DETECTOR ELEMENT IN A DIGITAL ANALOG OF THE CONVERTER AND BI-DIRECTIONAL COUNTER, THE ELEMENTS FOR THE DEFLECTION OF THE BEAMS BEING CONNECTED BY THE DIGITAL ANALOG CODE CONVERTER WITH THE OUTPUT OF THE BI-DIRECTIONAL COUNTER AN THE INPUTS OF WHICH ARE CONNECTED WITH THE OUTPUTS OF A CONTROL ELEMENT, WHICH TOGETHER WITH THE COUNTER FORMS THE COUPLINGS, A FIRST MEMORY ELEMENT FOR THE CONDITIONS THROUGH WHICH THE COUNTERS HAVE PROGRESSED, A SECOND MEMORY FOR THE SIGNAL EMITTED BY THE CONTROL ELEMENT WHICH IS ABLE TO CONTROL THE COUNTERS IN DEPENDENCY ON THE CONDITIONS AND ON THE SIGNAL, AND THE OUTPUT VOLTAGES OF THE COUNTERS DETERMINING THE COORDINATES OF THE POINTS OF A POINT RASTER WHICH IMPART THE POSSIBLE INTERSECTION POINTS OF THE BEAM WITH THE SCREEN. 